1. Field of the Invention
This invention relates to methods and devices for controlling the operation of the human heart or other organs by means of electrical stimulation, and more particularly, to devices for electronically slowing or stopping the heart.
2. Description of the Related Art
In some surgical procedures, such as coronary bypass surgery, it is necessary to stop the heart from beating so that the surgeon can perform necessary techniques. The use of a cardioplegia solution to stop the heart from beating without rerouting the blood would permit the surgeon to accomplish the required task without interference from heart movement. However, this is not a viable approach, since the body needs a constant supply of oxygen. Thus, there exists a need to temporarily slow down or stop heart movement during minimally invasive CABG or other surgical procedures to permit the surgeon to accomplish the required task. In the context of treatment of the heart by means of implanted medical devices, such as pacemakers, defibrillators and drug dispensers, it is also sometimes beneficial to slow or temporarily stop the heart, either for diagnostic or therapeutic purposes.
It has been known in the past to stimulate the vagal nerves by invasively dissecting the major nerve bundle and placing a spiral or enveloping nerve-type cuff around the nerve bundle. The nerve fibers are then directly stimulated by electrical field to achieve reduction in epilepsy, heart rate slowing, and potential blood pressure changes. In a study entitled “Selective Stimulation of Parasympathetic Nerve Fibers to the Human Sinoatrial Node”, Circulation, Vol. 85, No. 4, Apr. 1992, it was reported that cardiac parasympathetic nerve fibers located in an epicardial fat pad at the margin of the right atrium, the superior vena cava, and the right pulmonary vein in humans could be electrically stimulated to affect the heart rate. Additional reference is found in PACE October 1992 Vol. 15, No. 10, pt. 11, pages 1543-1630 on the use of nerve cuff stimulation of the vagal nerves (left side) in humans for reduction of epilepsy and it's side-effects. Additional uses for electrical nerve stimulation have been disclosed for the prevention of arrhythmias, alteration of hemodynamics, stimulation of the hypoglossal nerve for sleep apnea, stimulation of the stomach, and control of the sphincter for bladder or colon evacuation.
Currently, only nerve cuff-type electrodes or impalement-type electrodes are used for nerve stimulation, other than in the spinal cord. These types of electrodes can potentially cause irreversible nerve damage due to swelling or direct mechanical damage of the nerve. The placement of these electrodes either around the nerve bundle or into the neural perineum also poses a significant risk. The electrode placement is usually performed through very invasive surgery which in and of itself produces a high risk to nerve damage, and would be self-defeating when performing minimally invasive surgery. However, it has been demonstrated that the parasympathetic nerve fibers associated with the heart can also be stimulated by means of electrodes located on transvenous leads, as in U.S. Pat. No. 5,243,980, issued to Mehra et al, U.S. Pat. No. 5,507,784, issued to Hill et al and U.S. Pat. No. 5,356,425, issued to Bardy et al. The use of transvenous electrode leads to stimulate parasympathetic nerves associated with the heart is also discussed in the article “Neural effects on Sinus Rate and Atrial Ventricular Conduction Produced by Electrical Stimulation From a Transvenous Electrode Catheter in the Canine Right Pulmonary Artery, by Cooper et al., published in Circulation research, Vol. 46, No. 1, January 1980, pp. 48-57.
In conjunction with spinal cord stimulation, electrodes or electrode arrays located on pliant electrode pads are often employed. Recently, the ability to select from among various pairs of electrodes located on such electrode pads has been proposed to allow steering of the electrical field produced by the electrodes, as in U.S. Pat. No. 5,501,703, issued to Holsheimer, incorporated herein by reference in its entirety. Such electrode arrays offer additional possibilities to stimulate nerve fibers without direct and possibly damaging contact.